The present invention is directed to an improved zinc alloy, and in particular a zinc alloy suitable for hot chamber zinc die casting.
Hot chamber pressure die casting is generally preferred to the cold chamber method since it is far more productive and hence less costly than the cold chamber method. On the other hand, certain alloys, e.g. aluminum alloys, can only be die cast by the cold chamber method since they react with and degrade the materials of the die casting apparatus at temperatures used to hold them in their liquid state. When the mechanical properties of the alloy, e.g. creep resistance, are more important than cost, these alloys may be employed albeit by the cold chamber method.
Alloy compositions presently in use for hot chamber die casting include Zn/Al alloys containing about 4% Al. For example, a commercially available alloy is ZAMAK 5, which contains approximately 4% Al, 1.0% Cu, 0.04% Mg, the balance Zn. (All percentages are by weight.) The addition of Al to such alloys, however, causes the creep strength to degrade as the Al content exceeds about 1%.
Another alloy, ILZRO 16 (1.0-1.5% Cu; 0.15-0.25% Ti; 0.1-0.2% Cr; 0.01-0.04% Al; balance Zn) demonstrates high creep strength (presumably due to Ti-Cr-Zn precipitates) but is suitable only for cold chamber die casting.
It is, therefore, an object of the present invention to provide an alloy composition which is both suitable for hot chamber pressure die casting and has improved creep strength.